The present invention relates to a diaphragm carburetor for an internal combustion engine that operates with scavenging air, especially for the two-cycle engine in a manually guided implement such as a power chain saw, a cut-off machine, a trimmer, a brush cutter, or the like.
Manually guided implements such as power chain saws, cut-off machines, brush cutters, or the like are provided with a carburetor for producing a fuel/air mixture. For this purpose, fuel nozzles are provided in an intake channel portion of the carburetor that leads to the internal combustion engine; fuel enters the intake channel portion by means of such nozzles. The fuel nozzles, especially a main nozzle and an idling nozzle, are, with regard to their flow volume, measured such that during operation of the internal combustion engine that at least approximates stationary operation, a fuel/air mixture having a prescribed mixture ratio results in the engine. The fuel nozzles are supplied from a fuel-filled regulating chamber that is separated by a diaphragm from a compensation chamber, whereby the compensation chamber communicates with the clean air side of the air filter. The diaphragm regulates the quantity of fuel in the regulating chamber as a function of the air pressure on the clean air side of the air filter, so that the differential pressure between the regulating pressure and the intake channel portion remains constant, and the diaphragm carburetor operates independently of the pressure drop at the air filter.
The air channel or channels supply additional combustion air to the internal combustion engine and open directly into the combustion chamber. The supplied air serves as scavenging air, i.e. it displaces the exhaust gases out of the combustion chamber, separates the fuel/air mixture from the outlet, and simultaneously serves as additional combustion air. The quantity of the air supplied as scavenging air must be coordinated with the fuel/air mixture in the intake channel. For this purpose, the butterfly valve is coupled with the air valve or valves.
EP 1 026 390 A2 discloses a carburetor for a two-cycle engine and has an air channel with an air valve and a separate mixture channel with a butterfly valve, whereby the shaft of the air valve and the shaft of the butterfly valve are interconnected by means of a play coupling. The coupling permits a relative movement of the shafts relative to one another, whereby the magnitude of the angle of the play between the butterfly valve and the air valve is structurally prescribed by fixed abutments.
It is an object of the present invention to provide a diaphragm carburetor of the aforementioned general type that has a construction that is not sensitive to tolerances.